The present invention relates to lifeline systems and, particularly, to self-retracting lifeline systems including an energy absorbing mechanism or system.
The following information is provided to assist the reader to understand the invention disclosed below and the environment in which it will typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the present invention or the background of the present invention. The disclosures of all references cited herein are incorporated by reference.
Many devices have been developed in an attempt to prevent or minimize injury to a worker falling from a substantial height. For example, a number of devices (known alternatively as self-retracting lifelines, self-retracting lanyards, fall arrest blocks, etc.) have been developed that limit a worker's free fall distance to a specified distance and limit fall arresting forces to a specified value.
In general, most currently available self retracting lifeline safety devices or systems include a number of common components. Typically, a housing or cover provides enclosure/protection for the internally housed components. The housing includes attached thereto a connector for anchoring the self-retracting lifeline to either the user or to a fixed anchor point. The connector must be capable of withstanding forces required to stop a falling body of a given mass in a given distance.
A drum or spool around which a lifeline is coiled or spooled rotates within the housing. The drum is typically under adequate rotational tension to reel up excess extended lifeline without hindering the mobility of the user. Like the anchor connector and the other operative components of the retractable lifeline safety device, the drum is formed to withstand forces necessary to stop a falling body of a given mass in a given distance. The lanyard or lifeline is attached at one end thereof to the drum to allow the drum to reel in excess lifeline. The lifeline is attached at the other end thereof to either the user or to an anchorage point, whichever is not already attached to the housing.
Self-retracting lifeline systems also include a mechanism which locks (that is, prevents rotation of) the drum assembly of the self-retracting lifeline upon indication that a fall is occurring. For example, when the rope, cable or web being pulled from the self-retracting lifeline system causes the drum assembly to rotate above a certain angular velocity or experience an angular acceleration above a certain level, a brake mechanism can cause the drum assembly to suddenly lock.
Given the forces experienced by self-retracting lanyards upon sudden locking of drum rotation, the operational components of self-retracting lanyard are typically manufactured from high-strength materials such as stainless steel to ensure locking, while withstanding the stresses associated therewith. In that regard, though the fall may be stopped upon actuation of the braking mechanism of a self-retracting lanyard, the suddenness of the stop may cause injury to the user or produce higher than desirable stresses in one more components of the safety system.
In a low-cost variant of a self-retracting lifeline available under the name STOPMAX EVOLUTION™ from Antec of Vierzon, France (a division of Sperian Protection), a number of components, including the drum assembly are manufactured from low-strength polymeric materials. The drum assembly collapses or fails immediately and typically cinches the lifeline upon sudden locking of the braking mechanism in the case of a fall, resulting (like other self-retracting lanyards) in sudden stoppage of lifeline extension and substantial stresses.
Because of the substantial stresses that can result during a fall, some mechanism or method is typically used to absorb at least some of the energy of the fall. For example, on some self-retracting lifelines, the web itself has extra convolutions or folds that are held together by stitching which tears out to absorb energy. Other self-retracting lifelines use friction brake mechanisms to absorb the energy. Many mechanisms and/or methods of energy absorption used in currently available self-retracting lifelines require additional parts or assembly steps during manufacture which add cost, bulk and/or complexity to the self-retracting lifelines.
It is thus desirable to develop systems, devices and methods that reduce or eliminate the above and/or other problems associated with currently available self-retracting lifeline systems.